There is conventionally known that a press brake, which is a bending machine, ascends and descends a punch attached to an upper table relatively to a die attached to a lower table and thereby bends a workpiece in cooperation with the punch and the die. According to the conventional art, however, as shown in FIG. 1, if a workpiece W is set at a position offset in the longitudinal direction of a punch P and a die D, the workpiece W is to be so-called offset-bent. Due to this, a D-value (relative distance between the punch and the die) becomes non-uniform and a bending progress portion and a bending delay portion occur. Therefore, the conventional art has a disadvantage in that the passage angle of the workpiece W does not coincide with a target angle.
According to the conventional art, however, as shown in FIG. 1, if a workpiece W is set at a position offset in the longitudinal direction of a punch P and a die D, the workpiece W is to be so-called offset-bent. Due to this, a D-value (relative distance between the punch and the die) becomes non-uniform and a bending progress portion and a bending delay portion occur. Therefore, the conventional art has a disadvantage in that the passage angle of the workpiece W does not coincide with a target angle.
Furthermore, as shown in FIGS. 2A and 2B, if a part of the workpiece W is bent cooperatively by the punch P and the die D, an unbent portion is disadvantageously bent by the mutual influence of the punch P and the die D and the bending angle of a part of a bent portion disadvantageously decreases.
Meanwhile, as shown in FIG. 3, if the workpiece W is to be bent cooperatively by the punch P and the die D, the workpiece W is bent using a robot so as to follow up the spring of the workpiece W while clamping the workpiece by the workpiece clamper 101 of the robot or opening the workpiece clamper 101.
In this case, following the stroke position of the punch P, the position of the workpiece W when the workpiece W springs is subjected to a circular interpolation about of the shoulder section 103 of the die D and the follow-up coordinate of the workpiece clamper 101 of the robot is thereby calculated.
According to such conventional art, however, since the spring position of the workpiece is arithmetically operated based on the position of the die, the accurate workpiece spring position cannot be disadvantageously obtained. Further, since the conventional art cannot accurately deal with the bending speed and accurately follow up the bending speed in the end, “the buckling of the workpiece” and the like disadvantageously occur.
Furthermore, if bending is executed in a state in which pressure which horizontally acts on the workpiece is not uniform, whether offset bending or center bending, the right, center and left of the workpiece have different bending speeds. Due to this, even if a passage angle is eventually obtained, the workpiece is not always bent at a uniform insertion angle during the bending. Accordingly, if the robot or the like follows up bending, it is required to change the follow-up speed according to the clamp positions of the workpiece clamper 105, 107 and 109 as shown in FIG. 4, thereby disadvantageously making the operation quite laborious.
In view of the above-stated situations, the present invention has been achieved while paying attention to the conventional technical disadvantages stated above. It is, therefore, an object of the present invention to provide a bending method and a bending device capable of improving a bending passage angle by correcting a bending speed at a position in the longitudinal direction of a punch and a die.
It is another object of the present invention to provide a bending method and a bending device capable of accurately following up the spring of a workpiece using a robot.